Ohmic contact film in semiconductor device

ABSTRACT

The invention provides an ohmic contact film formed between a doped semiconductor material layer and a conductive material layer of a semiconductor device. The composition of the ohmic contact film according to a preferred embodiment of the invention is represented by the general formula M x Q z N y , where M represents the II group chemical element, Q represents the IV group chemical element, N represents the V group chemical element, 1≦x≦3, 1≦y≦3, 1≦z≦3, and x and y and z are molar numbers.

This application is a Division of currently pending application U.S. Ser. No. 11/797,851, entitled “OHMIC CONTACT FILM IN SEMICONDUCTOR DEVICE” and filed on May 8, 2007

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an ohmic contact film, and more particularly, to one formed between a doped semiconductor material layer and a conductive material layer of a semiconductor device.

2. Description of the Prior Art

Light-emitting diodes can be applied to various kinds of equipment, such as optical display equipment, regulatory signs, telecommunication equipment, and illuminating equipment. Light-emitting diodes, distinct from conventional light sources, are applicable to different industries.

The radiating principle of the light-emitting diodes is that the bonding of electrons and holes in the light-emitting layer of P-type and N-type semiconductors forms photons to generate light on forward bias. Because the P-type GaN semiconductor is hard to be doped, the contact of P-type GaN semiconductor and conductive layer produces higher resistance and consequently decreases the efficiency of P-type GaN semiconductor.

Taiwanese Patent No. 459,407 provides a proposal to reduce the contact resistance between a P-type GaN semiconductor layer and a conductive layer. Referring to FIG. 1, FIG. 1 illustrates a light-emitting diode structure having an n+ type reverse tunneling layer. The light-emitting diode structure includes an insulated sapphire substrate 11, a GaN buffer layer 12, an N-type GaN contact layer 13, an N-type AlGaN constraint layer 14, an InGaN light-emitting layer 15, a P-type AlGaN constraint layer 16, a P-type GaN contact layer 17, an n+ type reverse tunneling layer 18, a transparent conductive layer 19, a first electrode 21, and a second electrode 22. The GaN buffer layer 12 is formed on the insulated sapphire substrate 11. An N-type GaN contact layer 13 is formed on the GaN buffer layer 12 such that a partial area of the N-type GaN contact layer 13 is exposed. The first electrode 21 is formed on the exposed partial area of the N-type GaN contact layer 13. The N-type AlGaN constraint layer 14 is formed on the N-type GaN contact layer 13. The InGaN light-emitting layer 15 is formed on the N-type AlGaN constraint layer 14. The P-type AlGaN constraint layer 16 is formed on the InGaN light-emitting layer 15. The P-type GaN contact layer 17 is formed on the P-type AlGaN constraint layer 16. The n+ type reverse tunneling layer 18 is formed on the P-type GaN contact layer 17. The transparent conductive layer 19 is formed on the n+ type reverse tunneling layer 18 such that a partial area of the n+ type reverse tunneling layer 18 is exposed. The second electrode 22 is formed on the exposed partial area of the n+ type reverse tunneling layer 18 and contacts the transparent conductive layer 19.

The light-emitting diode improves the ohmic contact between the P-type GaN contact layer 17 and the transparent conductive layer 19 by adding an n+ type reverse tunneling layer 18 between them.

However, due to a complex manufacturing process and difficult control of the n+ type reverse tunneling layer 18, the finished products of light-emitting diodes are not stable and have a higher production cost as well.

Accordingly, a scope of the invention is to provide an ohmic contact film capable of improving the ohmic contact between the doped semiconductor material layer and the conductive material layer. Compared to the prior art, a semiconductor light-emitting device with the ohmic contact film has an easier manufacturing process; it also increases the stability for production and consequently has lower cost for production.

SUMMARY OF THE INVENTION

A scope of the invention is to provide an ohmic contact film formed between a doped semiconductor material layer and a conductive material layer of a semiconductor device. The composition of the ohmic contact film according to a preferred embodiment of the invention is represented by the general formula M_(x)N_(y), where M represents the II group chemical element, N represents the V group chemical element, 1≦x≦3, 1≦y≦3, and x and y are molar numbers. According to another preferred embodiment of the invention, an ohmic contact film is provided. The composition of the ohmic contact film is represented by the general formula M_(x)Q_(z)N_(y), where M represents the II group chemical element, Q represents the IV group chemical element, N represents the V group chemical element, 1≦x≦3, 1≦y≦3, 1≦z≦3, and x, y and z are molar numbers.

The advantage and spirit of the invention may be understood by the following recitations together with the appended drawings.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

FIG. 1 illustrates a light-emitting diode structure having an n+ type reverse tunneling layer.

FIG. 2 is the schematic sectional view of the ohmic contact film according to a preferred embodiment of the invention.

FIG. 3 is the drawing of the I-V test conducted for semiconductor light-emitting devices with and without the ohmic contact film.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, FIG. 2 is the schematic sectional view of the ohmic contact film 32 according to a preferred embodiment of the invention. The ohmic contact film 32 is formed between a doped semiconductor material layer 30 and a conductive material layer 34 of a semiconductor device. In practical application, the semiconductor device can be a semiconductor light-emitting device. The dopant type of the doped semiconductor material layer 30 can be N-type or P-type. The conductive material layer 34 can be Ni/Au, ITO, CTO, TiWN, In₂O₃, SnO₂, CdO, ZnO, CuGaO₂, or SrCu₂O₂.

The composition of the ohmic contact film 32 is represented by the general formula M_(x)N_(y), where M represents the II group chemical element, N represents the V group chemical element, 1≦x≦3, 1≦y≦3, and x and y are molar numbers. In practical application, the II group chemical element in the ohmic contact film 32 can be Zn, Be, Mg, Ca, Sr, Ba, or Ra. The V group chemical element in the ohmic contact film 32 can be N, P, As, Sb, or Bi.

In this embodiment, the ohmic contact film 32 is formed at a temperature ranging from 400° C. to 1100° C. The thickness of the ohmic contact film 32 is in a range of from 0.5 Angstroms to 500 Angstroms.

Refer to Table 1. Table 1 shows the results of a contact resistance test of a combination structure with and without the ohmic contact film 32. The combination structure includes a doped semiconductor material layer 30 of P-type GaN and a conductive material layer 34 of ITO. The ohmic contact film 32, formed between the P-type GaN and the ITO, has the composition of MgN, where Mg is selected from the II group chemical element, and N is selected from the V group chemical element. As shown in Table 1, the combination structure with MgN as the ohmic contact film 32 has a contact resistance lower than that without MgN by about an order. Therefore, the ohmic contact film 32 of MgN indeed improves the ohmic contact between the P-type GaN and the ITO.

TABLE 1 combination structure of P-type GaN and ITO contact resistance with MgN ohmic contact film 1.56 × 10⁻³ ohm-cm² without MgN ohmic contact film  2.5 × 10⁻² ohm-cm²

The calculation result in “Ferromagnetism in tetrahedrally coordinated compounds of I/II-V elements: Ab initiocalculations” of PHYSICAL REVIEW B 73 (2006) reveals that possible combinations of the II group chemical element and the V group chemical element have similar magnetic and electronic properties. It is found that all II-V compounds have a tendency toward a ferromagnetic ground state. On aspect of technology, it is believed that the ohmic contact film 32 according to the invention can be composed of other possible II-V compounds not mentioned in the specification of the invention.

Refer to FIG. 3. FIG. 3 is the drawing of an I-V test conducted for semiconductor light-emitting devices with and without the ohmic contact film 32. The ohmic contact film 32, included in the semiconductor light-emitting device, is prepared by the reaction between ammonia and Mg, and the composition of the ohmic contact film 32 is Mg₃N₂. As shown in FIG. 3, the semiconductor light-emitting device with Mg₃N₂ as the ohmic contact film 32 has a lower resistance value than that without Mg₃N₂.

According to another preferred embodiment of the invention, the composition of the ohmic contact film 32 in FIG. 2 is represented by the general formula M_(x)Q_(z)N_(y), where M represents the II group chemical element, Q represents the IV group chemical element, N represents the V group chemical element, 1≦x≦3, 1≦y≦3, 1≦z≦3, and x, y and z are molar numbers.

In practical application, the II group chemical element in the ohmic contact film 32 can be Zn, Be, Mg, Ca, Sr, Ba, or Ra. The IV group chemical element in the ohmic contact film 32 can be C, Si, Ge, Si, or Pb. The V group chemical element in the ohmic contact film 32 can be N, P, As, Sb, or Bi.

The experimental result, according to “Ab initio band structure calculations of Mg₃N₂ and MgSiN₂” of Condens. Matter 11, J. Phys (1999), proves that the energy gap of Mg₃N₂ is about 2.8 eV, while that of MgSiN₂ is about 4.8 eV. Because the energy gap width of Mg₃N₂ and MgSiN₂ is similar to that of InGaN, it is helpful to decrease the resistance value between the P-type GaN semiconductor material layer and the conductive material layer. Therefore, in the embodiment, the composition of the ohmic contact film 32 can be MgSiN₂.

The ohmic contact film according to the invention is capable of improving the ohmic contact between the doped semiconductor material layer and the conductive material layer. Compared to the prior art, the semiconductor light-emitting device with the ohmic contact film has an easier manufacturing process; it also increases the stability for production and consequently has lower cost for production. Moreover, from the technical viewpoint, the ohmic contact film provided by the invention is certainly applicable to other type of semiconductor devices not described in the specification.

With the example and explanations above, the features and spirits of the invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

1. An ohmic contact film formed between a doped semiconductor material layer and a conductive material layer of a semiconductor device, the composition of said ohmic contact film being represented by the general formula: M_(x)Q_(z)N_(y), and wherein M represents the II group chemical element, Q represents the IV group chemical element, N represents the V group chemical element, 1≦x≦3, 1≦y≦3, 1≦z≦3, and x and y and z are molar numbers.
 2. The ohmic contact film of claim 1, wherein the II group chemical element in said ohmic contact film is one selected from the group consisting of Zn, Be, Mg, Ca, Sr, Ba, and Ra, the IV group chemical element is one selected from the group consisting of C, Si, Ge, Si, and Pb, and the V group chemical element in said ohmic contact film is one selected from the group consisting of N, P, As, Sb, and Bi.
 3. The ohmic contact layer of claim 1, wherein said ohmic contact film is formed at a temperature ranging from 400° C. to 1100° C.
 4. The ohmic contact film of claim 1, wherein the thickness of said ohmic contact film is in a range of from 0.5 Angstroms to 500 Angstroms.
 5. The ohmic contact film of claim 1, wherein the dopant type of the doped semiconductor material layer is N-type or P-type.
 6. The ohmic contact film of claim 1, wherein the conductive material layer is formed of a material selected from the group consisting of Ni/Au, ITO, CTO, TiWN, In₂O₃, SnO₂, CdO, ZnO, CuGaO₂, and SrCu₂O₂. 